Jo Ann M. Gronberg20111130Map of Arsenic concentrations in groundwater of the United States2vector digital data Reston, Virginia U.S. Geological Surveyhttps://water.usgs.gov/lookup/getspatial?arsenic_mapMichael J. FocazioAlan H. WelchSharon A. WatkinsDennis R. HelselMarilee A. Horn1999A Retrospective Analysis on the Occurrence of Arsenic in Ground-Water Resources of the United States and Limitations in Drinking-Water-Supply Characterizationstabular digital dataWater-Resources Investigations Report 99-4279 99-4279https://pubs.usgs.gov/wri/wri994279/
The map graphic image at https://water.usgs.gov/GIS/browse/arsenic_map.png illustrates arsenic values,
in micrograms per liter, for groundwater samples from about 31,000 wells and springs in 49 states compiled
by the United States Geological Survey (USGS). The map graphic illustrates an updated version of figure 1
from Ryker (2001). Cited Reference: Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need,
but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36 at
http://www.agiweb.org/geotimes/nov01/feature_Asmap.html. An excel tabular data file, a txt file, along with
a GIS shape file of arsenic concentrations (20,043 samples collected by the USGS) for a subset of the sites
shown on the map. Samples were collected between 1973 and 2001 and are provided for download.
This map graphic image illustrates an arsenic point map created as an update to figure 1 from Ryker (2001)
because the legend from figure 1 was found to be ambiguous; value ranges, in micrograms per liter, for each
color overlapped at the end points (dark green: 1-3, light green: 3-5, yellow: 5-10, orange: 10-50, red: at least
50). Reproduction of the map revealed that the actual legend should be dark green: less than 3, light green:
3 to less than 5, yellow: 5 to less than 10, orange: 10 to less than 50, red: at least 50. The legend and map
were updated to more clearly identify points exceeding the U.S. Environmental Protection Agency arsenic
Maximum Contaminant Level of 10 micrograms per liter (dark green: less than or equal to 3, light green:
greater than 3 to less than or equal to 5, yellow: greater than 5 to less than or equal to 10, orange: greater
than 10 to less than or equal to 50, red: greater than 50).
The digital (excel and text and GIS) files contain 20,043 samples with station identification, location in
latitude and longitude, well depth, and arsenic concentrations collected by the USGS.
The map graphic image at https://water.usgs.gov/GIS/browse/arsenic_map.png is based on samples from
31,000 wells and springs in 49 states collected for studies on potable groundwater resources by the USGS,
the Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department
of Natural Resources, and the six New England states, New Hampshire, Vermont, Maine, Massachusetts,
Rhode Island, and Connecticut. The tabular data and GIS files in this data set exclude arsenic concentrations
from the non-USGS sources. Estimation of the arsenic concentration in groundwater in any specific area
must consider the following limitations and sources of variability:
1) The data include a variety of 20,043 well types, including private wells, public supply wells, and monitoring
wells not used for water supply.
2) These groundwater samples do not represent drinking water served by public water supply systems because
these utilities may treat or mix groundwater with high concentrations from individual wells to meet drinking water
standards before delivering it to consumers.
3) The appearance of the arsenic distribution is influenced by the order in which wells are plotted. In this map,
wells with higher concentrations are drawn on top of those with more moderate concentrations. This over-plotting
may exaggerate the frequency of high values in areas where wells are close together.
4) Arsenic concentration may vary with depth within the same aquifer, or between aquifers that are stacked
vertically - for example, a shallow sand and gravel aquifer can overly a deeper bedrock aquifer. The map does
not show the vertical distribution of arsenic.
5) Many of the wells were sampled more than once, but evaluation of the data indicates that there is no relation
between arsenic concentration and time for most of the wells; the most recent data point was usually selected
to represent a given well (Focazio and others, 2000).
With these qualifications in mind, the data provide an estimate of arsenic occurrence in the groundwater resource
in general. For additional detail on the studies behind the map, along with more detailed maps for portions of the
U.S., visit the USGS at http://water.usgs.gov/nawqa/trace/arsenic/index.html.
Cited and Related References:
Focazio, M.J., Welch, A.H., Watkins, S.A., Helsel, D.R., and Horn, M.A., 2000, A retrospective analysis on the
occurrence of arsenic in ground-water resources of the United States and limitations in drinking-water-supply
characterizations: U.S. Geological Survey Water-Resources Investigations Report 99-4279, 21 p.
Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine
of the Earth Sciences, v. 46 no. 11, p. 34-36.
Welch, A.H., Watkins, S.A., Helsel, D.R., and Focazio, M.J., 2000, Arsenic in ground-water resources of the
United States: U.S. Geological Survey Fact Sheet 063-00, 4 p.1973010100000020000330000000date range of dataCompleteNone planned-158.631946-66.99112268.14333425.39050USGS ThesaurusArsenicinlandWatersgroundwaterISO 19115 Topic CategorygeoscientificInformationinlandWatersenvironmentGeographic Names Information SystemUnited StatesData from Wisconsin, Minnesota, Texas, New Hampshire, Vermont, Maine, Massachusetts,
Rhode Island, and Connecticut should be obtained directly from the state agency. The downloadable data sets
excludes arsenic concentrations from the non-USGS sources.See Supplemental Information.U.S. Geological Survey, National Water-Quality Assessment ProgramNeil M. DubrovskyChief, Trace Elements National Synthesis Projectmailing and physicalCalifornia Water Science CenterCSUS Placer Hall6000 J StreetSacramentoCalifornia95819US916-278-3078916-278-3071nmdubrov@usgs.govhttps://water.usgs.gov/GIS/browse/arsenic_map.jpgMap of arsenic in groundwater of the United Statesgif
USGS arsenic data (20,043) was collected by Focazio and others (2000) and Welch and others (2000),
and updated by Ryker (2001). Ryker (2001) also utilized data retrieved from several state agencies: the
Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department
of Natural Resources, the New Hampshire Department of Environmental Services, the Vermont Department
of Environmental Conservation, the Maine Bureau of Health, Geological Survey, and Department of
Conservation, the Massachusetts Department of Environmental Quality, the Rhode Island Department of
Health, and the Connecticut Department of Health. USGS arsenic data can be accessed at
http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html. State data should be obtained directly
from the state agency.Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcGIS 10.0.3.3600Focazio, M.J., Welch, A.H., Watkins, S.A., Helsel, D.R., and Horn, M.A., U.S. Geological Survey20000101A retrospective analysis on the occurrence of arsenic in ground-water resources of the United States
and limitations in drinking-water-supply characterizationsU.S. Geological Survey Water-Resources Investigations Report99-4279Report and data available at https://pubs.usgs.gov/wri/wri994279/.Dubrovsky, N.M., U.S. Geological Survey20111130National Water-Quality Assessment Program, Trace Elements National Synthesis Project, Arsenic in groundwater of the United States Project web page available at http://water.usgs.gov/nawqa/trace/arsenic/index.html.Welch, A.H., Watkins, S.A., Helsel, D.R., and Focazio, M.J., U.S. Geological Survey20000501Arsenic in Ground-Water Resources of the United StatesU.S. Geological Survey Fact Sheet063-00Report available at https://pubs.usgs.gov/fs/2000/fs063-00/.Point features present.The map graphic image at https://water.usgs.gov/GIS/browse/arsenic_map.png represents 1973-2000
data retrieved from USGS and state agencies. There are areas where data are sparse. For example, Texas, Wisconsin,
Idaho, California, New Jersey, Minnesota, and Washington are represented by over 1000 wells; Rhode Island, Kentucky,
Mississippi, and New York are represented by fewer than 100 wells. The tabular excel and GIS data set contains 20,043
samples collected by the USGS. In addition, this data set includes only the most recent arsenic analysis available for
each well, at the time of retrieval (November 2001), and only analyses performed by hydride generation or Inductively
Coupled Plasma Mass Spectrometry (ICP/MS).
Ryker, S.J.20011101Mapping arsenic in groundwater--A real need, but a hard problemmapGeotimes Newsmagazine of the Earth Sciencesvol. 46, no. 11Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36. On line at: http://www.agiweb.org/geotimes/nov01/feature_Asmap.html.onLine1973010100000020000330date range of dataRyker (2001)mapRyker, S.J., U.S. Geological Survey20011101USGS arsenic data2, updated from Focazio and others (2000)spreadsheetOn line at: http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html.onLine1973010100000020000330date range of dataUSGS arsenic dataUSGS arsenic dataThe tabular data file of USGS arsenic data from Focazio and others (2000) and Welch and others (2000) was updated by Ryker (2001). Data were also supplemented by data retrieved from several state agencies: the Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department of Natural Resources, the New Hampshire Department of Environmental Services, the Vermont Department of Environmental Conservation, the Maine Bureau of Health, Geological Survey, and Department of Conservation, the Massachusetts Department of Environmental Quality, the Rhode Island Department of Health, and the Connecticut Department of Health. USGS arsenic data can also be accessed at http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html. State data should be obtained directly from the state agency.20010101000000U.S. Geological SurveySarah J. Rykermailing12201 Sunrise Valley Drive, Mail Stop 516RestonVirginia20192703-648-5210702-648-5792sjryker@usgs.gov
1) Figure 1 from Ryker (2001) is a map showing arsenic concentration, in micrograms per liter,
from groundwater wells in the United States, representing different concentration ranges by
different colors. This map was found to be ambiguous, because value ranges for each color
overlapped at the end points (3, 5, 10, 50). It was necessary to determine the actual legend
used and to see if it identified values exceeding the U.S. Environmental Protection Agency
(USEPA) arsenic Maximum Contaminant Level (MCL) of 10 micrograms per liter. At present
it was unclear if 10 was represented by yellow or orange.
2) Point feature "ident", which spatially represented the arsenic data from 31032 wells, was
retrieved from trace element archive for Ryker (2001). See earlier process step for data sources.
Determined that "ident" was a derivative of the point feature "wells31032", which was used in the
fig1_pts.aml creating the original figure 1 from Ryker (2001).
3) A map was produced using commands from fig1_pts.aml, which corresponded to the following legend:
dark green: <3, light green: >=3 to <5, yellow: >=5 to <10, orange: >=10 to <50, red: at least 50.
3) Verified that figure 1 from Ryker (2001) matched this map (from step 3) by overall visual inspection and
spot checking points at the end values, 3, 5, 10, and 50.
4) To more clearly identify points that exceed the USEPA arsenic MCL, a map was produced using the following legend:
dark green: <=3, light green: >3 to <=5, yellow: >5 to <=10, orange: >10 to <=50, red: >50.
5) arsenic_map.mxd was reviewed by Naomi Nakagaki and Donna Knifong to insure that the legend accurately
described the colored data points. Nakagaki ran statistics in INFO to verify that the number of values in each
category matched the "count" produced in ArcMap.
6) Metadata was reviewed by Naomi Nakagaki, Donna Knifong and Neil Dubrovsky.20111121000000U.S. Geological SurveyJo Ann M. GronbergHydrologistmailing345 Middlefield Road, Mail Stop 470Menlo ParkCalifornia94025650-329-4423650-329-4463jmgronbe@usgs.govVectorComplete chain66157Node, planar graph66613Albers Conical Equal Area29.545.5-96230.000000.00000coordinate pair0.0001000.000100MetersNorth American Datum of 1983GRS19806378206.4294.98arsenic_nov2001arsenic samples from potable groundwaterUSGSFIDInternal feature number.ESRISequential unique whole numbers that are automatically generated.ShapeFeature GeometryESRICoordinates defining the featuresSTAIDUSGS station identifierUSGSNaming convention for each USGS StationstringIdentifies each USGS Station16STATETwo-letter postal code for the U.S. state in which the sample was collected.U.S. Postal ServiceAL - WY, none = blankTwo-letter postal code for the U.S. state in which the sample was collected2FIPS5-digit county FIPS codeFederal Information Processing Standard01001 -56998, none = 0Federal Information Processing Standard state and county codes5LAT_DMSLatitude of well, in degrees, minutes, and secondsUSGSstringLatitude of well, in degrees, minutes, and seconds6LONG_DMSLongitude of well, in degrees, minutes, and secondsUSGSstringLongitude of well, in degrees, minutes, and seconds7WELLDEPTHDepth (below land surface) of finished well (may be less than total hote depth drilled) (feet)USGSintegerDepth (below land surface) of finished well (may be less than total hote depth drilled) (feet)10SAMPDATEDate water sample was collectedUSGSstringDate water sample was collected9SAMPTIMETime water sample was collectedUSGSstringTime water sample was collected5AS_RMRKRemark code qualifying the analytical result in AS_CONC.
For example, the combination of AS_RMRK="<" and AS_CONC="1" indicates that arsenic was not detectable at a laboratory reporting limit of 1 microgram per liter.
USGSstringRemark code qualifying the analytical result in AS_CONC. For example, the combination of AS_RMRK="<" and AS_CONC="1" indicates that arsenic was not detectable at a laboratory reporting limit of 1 microgram per liter.1AS_CONCConcentration of arsenic in sample, in micrograms per liter (ug/L) as arsenicUSGSnumberConcentration of arsenic in sample, in micrograms per liter (ug/L) as arseni1LAT_DDLatitude of well, in decimal degreesUSGSnumberLatitude of well, in decimal degrees12LON_DDLongitude of well, in decimal degreesUSGSnumberLongitude of well, in decimal degrees12The arsenic data (excel, text, and shape files) include USGS identification, location, well depth, sample date and arsenic concentration in micrograms per liter as arsenic. The arsenic data set contains the USGS data. State data should be obtained directly from the state agency.Ryker, S.J., 2001,
Mapping arsenic in groundwater--A real need, but a hard problem:
Geotimes Newsmagazine of the Earth Sciences, v. 46, no. 11, p. 34-36.
Updated from:
Focazio, M.J., Welch, A.H., Watkins, S.A., Helsel, D.R., and Horn, M.A., 1999,
A retrospective analysis on the occurrence of arsenic in ground-water resources
of the United States and limitations in drinking-water-supply characterizations:
U.S. Geological Survey Water-Resources Investigations Report 99-4279, 21 p.
U.S. Geological SurveyAsk USGS - Water Webserver Teammailing445 National CenterRestonVA201921-888-275-8747 (1-888-ASK-USGS)https://water.usgs.gov/user_feedback_form.html
Although these data have been used by the U.S. Geological Survey,
U.S. Department of the Interior, no warranty expressed or implied is
made by the U.S. Geological Survey as to the accuracy of the data.
The act of distribution shall not constitute any such warranty, and no
responsibility is assumed by the U.S. Geological Survey in the use of
these data, software, or related materials.
The use of firm, trade, or brand names in this report is for identification
purposes only and does not constitute endorsement by the
U.S. Geological Survey. The names mentioned in this document
may be trademarks or registered trademarks of their respective
trademark owners.shape filepartial coverageWinzip739 KBhttps://water.usgs.gov/GIS/dsdl/arsenic_nov2001_shp.zipexcel database filepartial coverageWinzip1,972 KBhttps://water.usgs.gov/GIS/dsdl/arsenic_nov2001_excel.zipexcel database filepartial coverageWinzip1,972 KBhttps://water.usgs.gov/GIS/dsdl/arsenic_nov2001_txt.zipNone. This dataset is provided by USGS as a public service.20140219U.S. Geological SurveyAsk USGS -- Water Webserver Teammailing address445 National CenterRestonVA20192USA1-888-275-8747 (1-888-ASK-USGS)https://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+arsenic_mapFGDC Content Standards for Digital Geospatial MetadataFGDC-STD-001-1998